This disclosure relates to wellbore completion and, in particular, but not exclusively, to methods and apparatus for running a completion string having a reaming tool into a pre-drilled well bore tool into a pre-drilled well bore. This disclosure also relates to a reaming tool having a specific geometric design within the reaming structure.
In the oil & gas exploration and production industry, in order to access hydrocarbons from a formation, a wellbore is typically drilled from surface and the wellbore lined with sections of metal tubulars. Many forms of tubulars may be used to line the wellbore including, for example plain solid walled tubulars, slotted tubular or tubulars comprising mesh screens and the like. Each tubular section is generally provided with threaded connectors, or otherwise joined, so that a number of the tubular sections can be joined together to form a string which is run into the wellbore.
A number of pipe “strings”, generally known as casing strings, may be inserted into the wellbore and suspended from the surface. The last casing string located in the wellbore which completes the wellbore may be known as the “completion string” and in contrast to the casing strings which are typically suspended from surface, the completion string may be suspended from within a selected position in the immediately previous casing string Following location of the completion string in the wellbore, the wellbore wall may be supported on, or collapse against, the outer surface of the completion string. The completion string may also be secured and sealed in place within the wellbore. For example, in the case of solid-walled tubulars, the annular space between the outer surface of the tubulars and the wellbore wall may be filled with a settable material such as cement and the completion string and cement may subsequently be perforated to provide hydraulic communication to the formation. In other examples, in the case of slotted tubulars or tubulars comprising screens, the annular space may be filled with gravel, sand or the like.
There are a number of difficulties associated with running a completion string into a wellbore and it is not unusual for the completion string not to reach the target depth on the first attempt to place it therein. For example, it is common for the completion string to encounter obstructions such as drill cuttings, ledges, swelling formations, wellbore collapses and the like which can make advancement of the casing or completion string more difficult or impossible. In other cases, the casing or completion string may become lodged or stuck in the wellbore, thereby preventing the casing or completion string from being easily retrieved or re-orientated.
Where difficulties in locating the casing or completion string proximate the target depth are encountered, if possible, the string may be withdrawn and/or the wellbore re-drilled or cleaned to remove obstructions. However, this is not always possible and, in such cases, the casing or string may be left in situ. Resolving such problems can be expensive and time-consuming. A reaming tool may be provided on the casing or completion string and the reaming tool may be rotated with the string to remove obstructions from the wellbore and permit progression of the string. However, completion strings are often not suited to transferring torque. For example, in order to improve flow of hydrocarbons through the completed string, it is desirable that the tubulars making up the string be as large a diameter as possible and the string may comprise expandable tubulars which are run into a wellbore and then plastically expanded to a larger diameter. However, larger diameter completion string tubulars typically have low torque capacity threads which are not suited to transfer of torque.
Completion strings are also being run into long horizontal or deviated wellbores in which, for example, the completion string must be advanced through a close fitting wellbore defining a highly tortuous path over several kilometers. As such, it may be very difficult to rotate the string due to friction losses. Also, the primary driving force used to locate the completion string at the target depth is often the weight of the string such that for long horizontal or deviated boreholes, the driving force to locate the completion string at target depth is provided by the weight of only a relatively short section of the string. Thus, in some cases, it may be difficult or impossible to either manipulate or locate the completion string.
Furthermore, completion strings are becoming more complex, having a elements directed to achieving a variety of functions in the wellbore. For example, a completion string may comprise a number of high cost elements, including slotted tubulars, expandable tubulars, self expanding elastomeric packers, sand screens, flow control devices, valves, and the like, many of which are inherently not suited to withstanding high levels of torque. This inhibits the ability and the desirability of transferring torque, tension or compression forces via the completion string.
Moreover, the application and location of flow control devices, valves, hydraulic liner hangers and the like are often dictated by the predicted reservoir performance calculated on the basis that the completion string is placed at the correct depth and in working condition. Thus, landing the completion string at the correct depth and in undamaged condition can be of critical importance to the utility of the well.
The completion string can thus be considered as a large diameter lightweight tubular which, in light of its vulnerability to high levels of vibration, torque and mechanical loads, is ideally placed in the wellbore without rotation.
International Patent Application Publication No. WO 2008/015402, incorporated herein in its entirety by reference describes running a string into a borehole. A reaming tool may be located on a distal end of the string, the reaming tool having a drive unit permitting a reaming structure of the reaming tool to be rotated relative to the string to facilitate reaming of the borehole without the requirement to rotate the string by application of torque thereto. The reaming tool drive unit may be powered by fluid, such as drilling mud or the like, and the fluid may be directed to the reaming tool from surface via the internal bore of the string. Such reaming tool may overcome many of the problems associated with running and operating a reaming tool with a string. However, with complex completion strings comprising tools such as sand screens, meshes, slotted liner and the like, such tools are typically porous or fluid-permeable which limits or prevents transfer of fluid through the completion string.
There is a need for improved fluid flow operated reaming tools for running completion strings, particularly in highly deviated wellbores.